Degreasing process



United States Patent 2,911,331 DEGREASING PROCESS Application May 31,1956, Serial No. 588,340

4 Claims. c1. 134-22 This invention relates to a vapor-phase degreasingprocess, and particularly to a method of degreasing, at relatively lowtemperatures, liquefied gas installations employed in the handling,storage and distribution of low temperature liquefied gases. The termliquefied gas installations will be used hereafter to mean all apparatussuch as storage tanks, trailers, Vaporizers, fractionation columns, etc.used in the manufacture,,handling, distribution and storage of lowtemperature liquefied gases such as liquid oxygen, liquid nitrogen,liquid argon and the like.

When liquefied gas installations such as liquid oxygen tanks have beenin service for a considerable time, there is an .accumulation of oil,grease and similar material on the' walls of the apparatus. Thisaccumulation is objectionable and troublesome if not removed.Heretofore, these accumulations have been eliminated by washing ICQ thefollowing detailed description and the accompanying drawing.

According to the present invention these objetcs are achieved byremoving the liquid content from the liquefied gas installation,establishing the temperature of said installation above the meltingpoint but below the boiling point of the degreasing solvent to be used,vaporizing said solvent, admitting the solvent vapors to theinstallation, condensing said vapors on the walls of the installation;withdrawing the condensed vapors containing the oil, grease and similarcontaminants removed from the walls of said installation, and purgingthe installation with a suitable dry gas such as nitrogen or air.

An important aspect of the invention resides in the selection of asuitable solvent. One such solvent that has been found to give excellentresults is trichloromono fiuoromethane "(i.e. CCl F) which has a meltingpoint of 168 F. and a boiling point of +75 F. Trichloromonofluoromethane is sold under the trade name Ferori 11 and will bereferred to hereinafter as such. Since Freon 11 has a melting point of--168 F., the applicant found that the cleaning cycle could be initiatedat about -l60 F. or slightly above the melting point of'the Freon 11. Itwas also discovered that removal of the residual Freon 11 from theinstallation could be affected by-simply purging the system with asuitable gas, pref;

with water soluble cleaners such as sodium metasilicate.

Briefly, this method of degreasing requires warming the system to atemperature above the freezing point of water (+32 F.), circulating alarge quantity of hot cleaning solution through the system, thoroughflushing of the system to remove all traces of washing solution,thorough drying by continued circulation of a hot inert gas to removeall-moisture from the system, and cooling the system before restoring itto service.

-If the system is not thoroughly washed and dried, the small lines maybecome clogged with undissolved salts fromthe wash solution or withparticles of ice formed by the freezing of free unremoved water.Furthermore, it is virtually impossible to analyze the large amount ofwash liquid employed in this method of degreasing for the relativelysmall quantityofoil and grease removed. In addition, the apparatus issusceptible to severe corrosion from the degreasing solvent, if saidsolvent is used in excessive concentrations. This is especially truewhen'installations of aluminum or copper are being cleaned.

'To service an installation having a 100,000 standard cubic. footcapacity would require approximately 75 man hours using the presentmethod of degreasing. A wash trailer having a 1500 gallon capacity isalso required to service such an installation and a supply of steam,water and electricity are needed to effect the desired cleaning. Withthe instant invention the same installation can be serviced in 10 /2hours and the only utility required is electricity.

"It is, therefore, an object of this invention to reduce thetime'required to clean low-temperature liquefied gas installations andto avoid some of the difficulties involved in the use of water solublecleaners.

Another object of this invention is to provide a method of degreasingliquefied gas installations wherein the cleaning operation may beinitiated at low temperatures.

' Another. object of this invention is to provide a method by whic h lowtemperature liquefied gas installations can he'efficiently'andeffectively cleaned with maximum simplicity'and a minimum of materialsand services.

These and other objects and advantages of the invention will be pointedout or will become apparent from erably heated to a temperature slightlyabove the'boiling point of the Freon 11. Moreover, Freon 11 isparticularly applicable for practicing the method of the instantinvention since it not only has low melting and boiling points, but isalso substantially noncombustible, nontoxic and inert.

It has likewise been discovered that several saturated and unsaturatedhalogenated derivatives of methane and ethane having melting pointsabout between 124 F. and 256" F. and boiling points about between +l87-F. and -41 F. may be used as solvents to practice the method of theinstant invention. These halongenated derivatives of methane and ethanecorrespond to the general formula: C H CI -F where w is one or two; x iszero or one; and y and z are integers of from zero to four. It isunderstood that the term integer as used'herein shall be construed toinclude zero.

The single figure of drawing illustrates diagrammatically one form ofsuitable apparatus to perform the cleaning operation. The apparatusconsists of a blower 1 to circulate nitrogen or air and a boiler 2 forvaporizing the solvent, with the necessary valves piping, etc. to carryout the process as described. This apparatus may be convenientlyinstalled on a trailer or other portable means to facilitate its use atvarious locations.

In carrying out the invention, the liquefied gas instal lation 3,represented diagrammatically as a liquid oxygen storage vessel, andhereafter referred to as such, is emptied of its liquid oxygen contentand connected at its top to the inlet line 4 and at its base to thereturn line 5 of the cleaning apparatus. When the vessel 3 has beenconnected to the cleaning apparatus, all valves throughout the systemare closed. Since the temperature depends somewhat on the particularsolvent used, the invention as hereinafter described in detail has beendescribed with reference to the temperature suited to the use of Freon11 as the solvent. It is understood that minor modifications would haveto be made to adapt the procedure to other solvents. To raise thetemperature of vessel 3 from about between 220 F. and ''297 F. to -'160F., dry gas is introduced into the system through valve 8 connected toany suitable source 'ofgas supply,'as for example, a cylinder ofnitrogen, herein not shown. Residual oxygen is then purged from theinstallation by admitting nitrogen to the system through valves 8 and 9.The nitrogen is carried by Patented Nov. 3,' 1 9 l w M g,911,3s1

line 4 to the storage vessel 3 and is exhausted to the atmospherethrough return line 5 and valve 12. procedure is necessary in order toremove residual oxygen and solids such as CO which may contain acetyleneor other hazardous material. When nitrogen is exhausting freely fromvalve 12, valves 8 and 12 are closed and valve 19 is .opened. The bloweris then started and nitrogen is circulated in a closed system. Pressuregauge 14 located downstream of blower 1 indicates the pressure in thesystem at this stage of operation and valve 9 located downstream ofgauge 14 is provided as a throttling means to maintain the system atapproximately 5 p.s.i.g. If the system requires additional gas, it maybe admitted through valve 25, likewise connected to a suitable source ofgas supply. The heat of compression in the blower results in a rise intemperature of the circulated gas passing through said blower. This risein temperature serves in turn to heat the liquid installation. Iftempera ture gauge 15 located upstream .of blower 1 indicates that thegas from the storage vessel 3 is too cold, valve 6 may be partiallyopened to recirculate a portion of the warm gas directly to the blower.Also, if there is ample dry gas available for addition to the system,.cold gas may be discharged at valve 12.

When the temperature .of gas from the storage vessel 3 is warmed toabout l 60 F., as indicated by temperature gauge 10, located in returnline 5 downstream of storage vessel 3, all valves throughout the systemare closed. The nitrogen is then disconnected from valve 8. Valves 8 and19' are then opened and a partial vacuum is pulled on the storage vesselby throttling the system at valve 9 and using the blower 1 as a vacuumpump. Pressure gauge 13 upstream of blower 1 will indicate the extent ofthe vacuum obtained, either as limited by the design conditions of thevessel being cleaned or the maximum of the blower. When said vacuum hasbeen obtained, all valves throughout the entiresystem are closed.

A suitable solvent is admitted to the boiler 2 through valve 16 andheater 1! is started in order to vaporize the solvent. When the pressureindicated at pressure gauge 18 rises to 5 p.s.i.g., valve 7 is opened.Solvent vapor is passed through valve 7 and inlet line 4 to the storagevessel 3 where it condenses on the walls of said vessel, washing it asit runs down the walls and collects in the bottom of the vessel. Theoil-contaminated solvent is returned to the boiler 2 byway of valve 11through return line 5. When liquid samples taken at valve 12 indicatethat the vessel is clean, the heater 17 is shut ofi, the Freon boiler zis shut down and valves 7 and 11 are closed. Valves 9 and 19 are thenopened, blower 1 is started and circulation of nitrogen is commencedwith said nitrogen introduced at valve 25. When the pressure at gauge 14falls below 5 p.s.i.g., additional nitrogen is introduced at valve 25;all other valves must ,be closed when this step is initiated and valve 9may be used as a throttling means to maintain the system at 5 p.s.i.g.If the temperature of the gas coming to blower 1 from storage vessel 3should be too cold, as indicated by temperature gauge 15, a portion ofthe warm circulating gas from the blower may be returned to the blowerthrough valve 6. The remaining condensed solvent is then returned toboiler 2 through valve 11. Qirculation of nitrogen-containing residualsolvent vapor is continued until temperature gauge shows that the vessel'3 is warmed to a temperature above the ambient air temperature. At thispoint the nitrogen :is disconnected from valve 25. Valve 25 is thenopened to the ambient air, valves 3 and 11 are closed and valve 12 isopened as an exhaust to the atmosphere. Warm am- .oient air is blowninto the vessel 3 by blower 1, past .valve 9, through inlet line 4 tothe storage vessel 3 and i ex au e th u h e u n l n 5 an valv 12- hinece sar 0 e t s mul tesam ent ai to a temperature above the temperatureof the system before admitting it to vessel 3. In operation the normallyheated to about F. by the heat of compression of the blower. If vessel 3isffcolder than the ambient air, condensation of the moisture in the airwill take place on the walls of the vessel. When all lines of the systemare blowing free and warm, the vessel is ready to be restored toservice. Nitrogen and are inert with respect to both the storage vessel3 and the liquid oxygen in the vessel. The term inert drying gas as usedherein shall be construedto mean a drying gas which is inert h r pe t hest lla n r u ms t an 1 t liquefied gas contained therein, and not adrying gas which is inert per se.

While the instant invention is especially eflective for degreasingliquefied gas installations generally operated at temperatures aboutbetween 220 F. and 320 F., it will be obvious to those skilled in theart that said method of degreasing may also be used to cleaninstallations operated at temperatures about between 0 F. .-220 F.

While only one embodiment of the invention has been shown and describedherein, his to be understood that the invention is not limited to theparticular form shown, but may be use din other ways without departurefrom its spirit as defined by the following claims.

What we claim is:

1 A method of degreasing a liquefied gas installation with a degreasingsolvent which comprises removing the liquefied gas from saidinstallation, adjusting the temperature of the liquefied .gasinstallation to a temperature above the melting point but below theboiling point .of said solvent, admitting said solvent vapor phase tosaid installation whereby said vapors condense on the walls of saidinstallation at said temperature and dissolve the soluble materials fromsaid walls while gravitating to the bottom of said installation, saidsolvent being selected from a group consisting of saturated andunsaturated halogenated derivatives of methane and ethane having meltingpoints about between .124 F. and -256 F. and boiling points aboutbetween +187 F. and 41 F., withdrawing said condensed vapors C9D:taining said materials therefrom, and removing moisture from saidinstallation by passing therethrough an mert drying gas in an amounteffective to removesaid moisture.

2. The method according to claim 1 in which said degreasing solventcorresponds to the general formula: ,C H Cl F where w is an integer fromone to two; x is an integer from zero to one; y and z are integers fromzero to four; and the sum of W, y, n Z 91 4 #93 five to eight.

3. The method according to claim 1 in which said degreasing solvent istrichloromonofluoromethane.

4. A method of degreasing a liquefied gas installation comprisingremoving the liquefied gas from sa d installation, heating saidinstallation to a temperature of about F., admittingtrichloromonofluoromethane n vapor phase to said installation wherebysaid vapors condense on the walls of said installation at saidtemperatute and remove grease and like materials .theref romas saidcondensed'vapors gravitate to the bottom of said mstallation. removing sd c d ns d vapors onta m amas and like materials from said installation,and purging said installation by the passage therethrough of drynitrogen followed by air, the temperature of the air being above thetemperature of the nitrogen.

References Citedin the fileof this patent UNITED STATES PATENTS

1. A METHOD OF DEGREASING A LIQUEFIED GAS INSTALLATION WITH A DEGREASINGSOLVENT WHICH COMPRISES REMOVING THE LIQUEFIED GAS FROM SAIDINSTALLATION, ADJUSTING THE TEMPERATURE OF THE LIQUEFIED GASINSTALLATION TO A TEMPERATURE ABOVE THE MELTING POINT BUT BELOW THEBOILING POINT TO SAID SOLVENT, ADMITTING SAID SOLVENT IN VAPOR PHASE TOSAID STALLATION WHEREBY SAID VAPORS CONDENSE ON THE WALLS OF SAIDINSTALLATION AT SAID TEMPERATURE AND DISSOLVE TO THE BOTTOM OF SAIDINSTALLATION, SAID SOLVENT BEING SELECTED FROM A GROUP CONSISTING ODSATURATED AND UNSATURATED HALOGENATED DERIVATIVES OF METHANE AND ETHANEHAVING MELTING POINTS ABOUT BETWEEN-124* F. AND -256* F. AND BOILINGPOINTS ABOUT BETWEEN +187* F. AND -41* F., WITHDRAWING SAID CONDENSEDVAPORS CONTAINING SAID MATERIALS THEREFROM, AND REMOVING MOISTURE FROMSAID INSTALLATION BY PASSING THERETHROUGH AN INERT DRYING GAS IN ANAMOUNT EFFECTIVE TO REMOVE SAID MOISTURE.